A conventional maximum torque-current ratio control method is described in “Wide Speed Control of Interior Permanent Magnet Synchronous Motor” Journal of The Institute of Electrical Engineers of Japan, Vol. 114-D, No. 6, '94 p. 668, in which a motor constant and a q-axis current value are used to generate a d-axis current value and the reluctance torque of the motor is fully used to minimize current at the same torque.
[Non-patent Document 1] “Wide Speed Control of Interior Permanent Magnet Synchronous Motor” Journal of The Institute of Electrical Engineers of Japan, Vol. 114-D, No. 6, '94 p. 668.